Cocoa flavanols (CF) influence physiological processes in ways that suggest their consumption may improve aspects of neural function, and previous studies have found positive influences of CF on cognitive performance. In this preliminary study we investigated whether visual, as well as cognitive, function is influenced by an acute dose of CF in young adults. We employed a randomized, single-blinded, order counterbalanced, crossover design in which 30 healthy adults consumed both dark chocolate containing 720mg CF and a matched quantity of white chocolate, with a one week interval between testing sessions. Visual contrast sensitivity was assessed by reading numbers that became progressively more similar in luminance to their background. Motion sensitivity was assessed firstly by measuring the threshold proportion of coherently moving signal dots that could be detected against a background of random motion, and secondly by determining the minimum time required to detect motion direction in a display containing a high proportion of coherent motion. Cognitive performance was assessed using a visual spatial working memory for location task and a choice reaction time task designed to engage processes of sustained attention and inhibition. Relative to the control condition, CF improved visual contrast sensitivity and reduced the time required to detect motion direction, but had no statistically reliable effect on the minimum proportion of coherent motion that could be detected. In terms of cognitive performance, CF improved spatial memory and performance on some aspects of the choice reaction time task. As well as extending the range of cognitive tasks that are known to be influenced by CF consumption, this is the first report of acute effects of CF on the efficiency of visual function. These acute effects can be explained by increased cerebral blood flow caused by CF, although in the case of contrast sensitivity there may be an additional contribution from CF induced retinal blood flow changes.
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